This invention relates generally to the field of endodontic instruments and more particularly to reamers or files used in performing root canal procedures. The reamers are used to remove diseased tissue from the canal prior to sealing and filling the canal cavity with a suitable filler material, such as gutta-percha.
One of the more technically difficult and delicate procedures in the field of dentistry is root canal therapy. The root canal of a tooth houses the circulatory and neural systems of the tooth. These enter the tooth at the terminus of each of its roots and extend through a narrow, tapered canal system to a pulp chamber adjacent the crown portion of the tooth. If this pulp tissue becomes diseased or injured, it can cause severe pain and trauma to the tooth, sometimes necessitating extraction of the tooth. Root canal therapy involves removing the diseased tissue from the canal and sealing the canal system in its entirety. If successful, root canal therapy can effectively alleviate the pain and trauma associated with the tooth so that it need not be extracted.
To perform a root canal procedure, the endodontist first drills into the tooth to locate the root canal and then uses instruments of small diameter such as reamers and files to remove the decayed, injured or dead tissue from the canal. These are tapered instruments used to remove the diseased tissue in the root canal by reciprocating and/or rotating motion. The primary goal is to remove all of the decayed or injured nerve while leaving the integrity of the root canal walls relatively unaffected. Preserving the integrity of the root canal is important in order to allow proper filling of the root canal void in a homogenous three dimensional manner such that leakage or communication between the root canal system and the surrounding and supporting tissues of the tooth is prevented. Once as much of the diseased material as practicable is removed from the root canal, the canal is then sealed closed, typically by reciprocating and/or rotating a condenser instrument in the canal to urge a sealing material such as gutta-percha into the canal.
Since root canals are not necessarily straight and are often convoluted, it is often difficult to clean the canal while preserving its natural shape. Many instruments have a tendency to want to straighten out the canal or proceed straight into the root canal wall, altering the natural shape of the canal and sometimes transporting completely through the canal wall. Also, the opening of many root canals are small, particularly in older patients, due to calcified deposits on the root canal inner walls. Thus the files or reamers must be able to withstand the torsional load necessary to penetrate and enlarge the canal for purposes of treatment without breaking the instrument. A similar requirement exists for compactors or condensers used to fill the root canal with gutta percha. Gutta-percha used as a sealing material has a high viscosity and thermoplastic character. It is desirable, therefore, to use a condenser instrument that is able to withstand the torsional load necessary to urge the material into the canal without breaking the instrument while at the same time condensing the sealing material without leaving any voids in the canal which may lead to treatment failure.
One of the problems with traditional endodontic instruments used for extirpating and filling a root canal is that the torsional limitations of the instrument are often exceeded resulting in breakage of the instrument. Breakage of the instrument may occur as a result of the inadequate removal of dental chips which are cut from the wall of the root canal. The dental chips may be engaged between the instrument and the root canal wall resulting in friction which may cause excessive torque and thus breakage of the instrument.
Traditional reamers or files contain helical flutes along the working portion which are substantially semicircular in cross-section, that is, an arc tracing a line transverse to the flute length along the bottom of the flute wall is of substantially uniform radii at all points along the line. This structure is intended to promote advancement of tooth chips and debris up the expanding diameter of the instrument along the spiraling flute away from the tip. However, during the extirpating procedure, the dental chips which are formed may be inadequately removed from the root canal and may be forced into flutes along the instrument between the instrument and the root canal causing damage to the canal walls and/or inadequate or uneven tissue removal. This build up of debris may also lead to increased friction resistance already imposed by contact between the instrument and the canal, which in turn increases the torsional load on the instrument. In many cases, the torsional loads on the instrument exceed the tensile strength of the working portion of the instrument resulting in fracture.
Another problem that can occur is transportation or penetration through the canal wall. This can occur when a straight file or reamer is used to prepare a curved canal. The file often will want to maintain a straight path into the root canal wall instead of following the natural path of the canal. In some extreme cases, the file can actually perforate the wall of the root canal causing injuring of the supporting tissues of the tooth. One attempt to solve this problem is to provide a dental file having a smooth-walled non-cutting pilot tip for guiding the file or reamer into the curved root canal. See, for instance, U.S. Pat. No. 4,299,571 to McSpadden, incorporated herein by reference. While the provision of such a smooth-walled pilot tip represented a significant improvement in the art at the time, the design has significant drawbacks in certain cases.
The primary drawback is that the pilot tip, being blunt and smooth, has little or no cutting ability. While the blunt tip can fairly easily wedge its way into the soft, fleshy nerve, there is often difficulty encountered in a calcified root canal which has layers of calcified accretion built up along the inner wall of the canal. It is often difficult in these highly calcified root canals to penetrate through the calcified material to a depth sufficient to allow cutting to begin. When using such files having a blunt tip, the file must essentially burnish or grind its way into the calcified material before entering the canal. This generates significant heat and friction as the tip attempts to burnish its way through the hard calcified material. This can cause pain and heating of the tooth which is undesirable. It can also cause increased torsional loads on the file or reamer which can increase the risk of breakage in the canal and decreases the life of the tool.
The present invention is directed to an improved endodontic instrument for use in an endodontic root canal procedure which comprises an elongate working portion having a length of from about 3 to about 18 millimeters, a peripheral diameter ranging from about 0.08 millimeters to about 1.9 millimeters, at least one helical flute, at least one helical land and at least one tissue removing edge. Each flute and land has a pitch ranging from about 1 spiral per 16 millimeters to about 1 spiral per millimeter.
In accordance with one preferred embodiment, the above-described working portion has a chisel tip portion at the end of the working portion. The chisel tip portion comprises plural facets which intersect along a substantially linear chisel edge that is substantially orthogonal to a longitudinal axis of the elongate working portion.
In another preferred embodiment, the chisel tip portion comprises plural facets which intersect along a substantially linear chisel edge such that upon rotation of the tip portion in the root canal, each of the facets removes tissue along respective removing edges that are substantially collinear with each other along the chisel edge.
A further aspect involves a chisel tip portion at the end of the previously described working portion. The chisel tip portion comprises plural facets which intersect along a chisel edge. The facets intersect the working portion at respective tissue removing edges disposed at the periphery of the working portion. The tissue removing edges are unequally spaced about the periphery. Preferably, the flute is in working cooperation and adjacent to the land so as to provide a tissue-removing edge therebetween, and the working portion through provision of one or more friction reducing elements is adapted to reduce friction between the instrument and the canal walls to improve the performance of the instrument while reducing the tendency of the instrument to fail under torsional stress.
In one friction reducing embodiment, the point distal from the tissue-removing edge adjacent the periphery, in cross-section, recedes from the periphery at from about an acute angle with respect to a line tangent to the periphery at the point of intersection. The angle is measured from the side of the tangent line distal from the tissue-removing edge.
In another embodiment, the endodontic instrument has at least one outer land, when viewed in cross-section, adjacent the periphery defined by the tissue-removing edge and at least one recessed land. The outer land and the recessed land may be adjacent one another or separated by one or more flutes.
In yet another embodiment, the endodontic instrument comprises at least two flutes spaced apart by a tissue-removing edge or a land which flutes or lands have substantially unequal dimensions when viewed in cross-section. An endodontic instrument may also comprise a combination of two or more of the foregoing preferred embodiments.
These and other features and advantages will be readily apparent to those skilled in the art, having reference to the following detailed description and accompanying drawings, the invention not being limited to any one preferred embodiment.